CONCORD, N.H. (AP) — Two oil companies that failed to reach a settlement with the state of New Hampshire over groundwater contamination caused by a gasoline additive have chosen to go trial.

The Concord Monitor (http://bit.ly/VSgyZg ) says the lawsuit pitting New Hampshire against ExxonMobil and Citgo goes to trial Monday in Merrimack County Superior Court.

The lawsuit, filed in 2003, contends the gasoline additive MTBE contaminated groundwater by seeping into thousands of drinking water supplies in New Hampshire. The additive helped to comply with the Clean Air Act but the state banned it in 2007 after it was found in groundwater.

Twenty-four oil companies and refineries already have settled for about $120 million. The vast majority of the settlement money has gone to cleanup.